Note that this is not something I would recommend in a production environment!
But, for example, in a demo environment this can be useful to save some disk space 🙂
So, whenever you’ve installed a Service Pack to a Windows OS (w2k8 R2 or higher) some installation files are left behind. This is so that you can remove it. So when you remove these installation files, you can’t turn back (without a backup of course…).
You can use the DISM tool to remove the Service Pack installation files and with that make the Service Pack installation permanent:
dism /online /cleanup-image /spsuperseded